Small issue. Not a biggie, just an annoyance. I have 4, Dell T5810 workstations running W10, with indentical mobo & CPU. On 3 of them, FF starts in ~1 second. On the other, it takes ~ 10 seconds to start (and of course, it's the one I use most ). I've fussed with disabling all the add-ons (which are about the same on all 4), doing a fresh FF install (including deleting old profile) and even running a utility to "align partition" of the drive (which, afterwards, the computer would not boot... so reverted to the "non aligned" state). When I start Pale Moon browser on the "trouble" machine, it also boots in 1 sec. Got ideas on what to try next?
Have you tried other browsers? Do they start slowly too? Either way, I recommend cleaning out your temp files and cookies.
Just check for some other alternatives. I prefer not to rely on a single browser all the time. Also, if others are also working slow, then most probably the issue is in your system.
People have their preferences. I mean, I prefer Firefox even though I have Chrome too, and whatever Microsoft's current browser is called. If Firefox wasn't working properly I'd be doing my best to fix it, rather than move onto Chrome.